The present invention relates to a pump circuit which, for example, is applied to a semiconductor integrated circuit, such as a dynamic RAM and a flash EEPROM, and generates a voltage higher than the supply voltage in the semiconductor integrated circuit.
Recently, low power consumption in semiconductor integrated circuits has been required, and according to this demand a supply voltage has been lowered. However, there are circuits that require a voltage higher than a supply voltage in a semiconductor integrated circuit. By this reason a so-called charge pump circuit is provided for boosting the supply voltage to a predetermined voltage in the semiconductor integrated circuit, and the voltage boosted by the pump circuit is supplied to the circuit requiring a high voltage.
FIG. 29 shows an example of a conventional charge pump circuit. This charge pump circuit constituted of an inverter circuit IV to which an input signal Sin is supplied, a capacitor C as a coupling capacitor whose one end is connected to an output terminal of the inverter circuit IV, and N-channel transistors TN1, TN2 connected to the other end of the capacitor C. The inverter circuit IV is composed of a P-channel transistor TP1 and an N-channel transistor TN3. In this circuit, the voltage of a node ND1 is transmitted to a node ND2 via the capacitor C so as to boost the voltage of the node ND2.
FIG. 30 is waveforms showing operations of FIG. 29. The transistor TN1 is activated at a time t1, and the node ND2 is precharged to a supply voltage Vcc via the transistor TN1. After this, the input voltage Sin is made a low level at a time t2. Accompanied with this, the node ND1 is made the supply voltage Vcc via the inverter circuit IV. Then, the electric potential of the node ND2 is boosted to 2 Vcc via the capacitor C. Next, at a time t3, the transistor TN2 is activated, and the electric potential of the node ND2 is output as a boosted voltage Vpp via the transistor TN2. After this at a time t4 the input voltage Sin is made a high level, and the inverter IV is inverted.
By the charge pump circuit shown in FIG. 29, a required boosted voltage Vpp can be generated. However, this circuit has a problem of a low current efficiency, that is, a high current consumption.
For example, as a method for improving the current efficiency of the charge pump circuit shown in FIG. 29, there is a pump circuit described in xe2x80x9cAn Efficient Charge Recycle and Transfer Pump Circuit for Low Operation Voltage DRAMs, Takeshi Hamamoto et al., 1996 Symposium on VSL1 Circuit Digest of Technical Papers.xe2x80x9d This circuit is constituted, for example, using a plurality of charge pump circuits as shown in FIG. 29, and the improvement of the current efficiency is attempted by recycling electric charge of the capacitors of the charge pump circuits.
FIG. 31 shows a conventional two-phase charge recycle pump circuit constituted using two pump circuits resembling the pump circuit described in the above mentioned literature. (In this two-phase charge recycle pump circuit, electric charge is transmitted through one path from a node with a high electric potential to a node with a low electric potential. Thus, this circuit is called two-phase serial charge recycle pump circuit.) Attaching numerals 1, 2 are added to the same symbols of the same parts in FIG. 31 as those in FIG. 29. In this circuit, a transistor TN4 is connected to charge coupling nodes ND11, NQ12 of capacitors C11, C12 each another. The electric charge of these nodes ND11, ND12 is recycled via the transistor TN4.
FIG. 32 shows waveforms showing operations of the circuit shown in FIG. 31. As shown in FIG. 32, in the circuit shown in FIG. 31, a P-channel transistor TP1 is turned on according to a precharge signal PRE, and the node ND11 is precharged to the supply voltage Vcc. An equalizing signal EQ is activated, and an N-channel transistor TN4 is turned on, whereby the electric potentials of the node ND11 and the node ND12 are made equal. That is, a half of the electric charge of the node ND11 is transferred to the node ND12.
With this, in the circuit shown in FIG. 31, since the electric charge of the nodes ND11, ND12 is recycled by the N-channel transistor TN4 operated according to the equalizing signal EQ, the current efficiency is improved. However, in the case of two-phase charge recycle pump circuit, the fluctuations of the voltages of the nodes ND11, ND12 are decreased to 0.5 Vcc. Thus, the maximum voltage of the boosted voltage Vpp that can be output is reduced from 2 Vcc of the conventional to 1.5 Vcc.
FIG. 33 shows a conventional four-phase charge recycle pump circuit (four-phase serial charge recycle pump circuit) in which capacitors and transistors are further added to the circuit shown in FIG. 31, and FIG. 34 shows waveforms illustrating operations of the circuit shown in FIG. 33. In the case of four-phase charge recycle pump circuit, the electric charge of the node ND11 is transferred to other nodes one after another according to the equalizing signal EQ and the precharge signal PRE. Accordingly, since the recycle frequency of the four-phase charge recycle pump circuit is higher compared with the two-phase charge recycle pump circuit, a utilization efficiency of current is improved so as to enable power-saving. However, in this pump circuit, the maximum voltage of the boosted voltage Vpp is reduced from 2 Vcc of the conventional to 1.25 Vcc.
In the case where the number of steps of a pump circuit is increased so as to obtain an n phase, when a maximum voltage Vpp is in vicinity of a supply voltage Vcc, a maximum current efficiency is increased to a level of 1/[1+(1/n)]. However, a maximum boosted voltage is decreased to 1/[1+(1/n)]Vcc. Accordingly, there is a problem that a high voltage cannot be output and efficiency is reduced in a high voltage area compared with a conventional pump circuit.
FIG. 35 shows an improved pump circuit of the circuit shown in FIG. 31. This pump circuit is a conventional two-phase charge recycle pump circuit in which the electric charges charged in charge coupling nodes of two capacitors are mutually recycled. (In this two-phase charge recycle pump circuit, electric charge is transmitted bidirectionally from an arbitrary node with a high electric potential to a node with a low electric potential. Thus, this circuit is called two-phase parallel charge recycle pump circuit.) FIG. 36 is waveforms showing operations of FIG. 35.
In this pump circuit, the nodes NQ12, ND11 are alternately precharged to a supply voltage Vcc according to precharge signals PRE1, PRE2. Then, the nodes ND11, ND12 are equalized by an N-channel transistor TN4 turned on according to the equalizing signal EQ. According to this equalizing operation the electric charges of the nodes ND11, NQ12 are recycled. That is, electric charge is transferred from a node with a high electric potential to a node with a low electric potential by the operation that the nodes ND11, NQ12 precharged to the supply voltage Vcc are equalized, whereby the electric charges remaining in each node ND11, ND12 are recycled. Then, current is supplied from a power supply to the node where electric potential is boosted, and the node where electric potential is lowered is grounded. Operations like this are repeated so as to generate a high voltage.
However, in each conventional charge recycle pump circuit described above, electric charge is not fully recycled. For example, in the case of the circuit shown in FIG. 35, the electric charges of the nodes ND11, ND12 are recycled only once. That is, the electric charge transferred in one recycle is the half of the electric charge remaining in each node, and the remaining xc2xd electric charge is not utilized. By this reason a large amount of current is required in order to obtain a high output voltage, thereby causing difficulty in obtaining a satisfactory current efficiency.
The present invention is to solve the above described problems, and it is an object of the present invention to provide a pump circuit in which a desired high voltage can be obtained by effectively utilizing the electric charge charged in a charge coupling node of a capacitor so as to improve the current efficiency.
An object of the present invention is achieved through a pump circuit comprising: at least three capacitors each having a first node and a second node; a plurality of first transistors connected between the first nodes of the respective capacitors and a first power supply, the first transistors charging the first nodes, respectively; a plurality of second transistors connected between the second nodes of respective the capacitors and the first power supply, the second transistors charging the second nodes, respectively; a plurality of third transistors connected between the second nodes of respective the capacitors and an output terminal, the third transistors outputting the electric charge of respective the capacitors to the output terminal; and a plurality of fourth transistors connected between the first nodes of respective the capacitors, the forth transistors sharing control signals with the first transistors corresponding thereto.
An object of the present invention is achieved through a pump circuit comprising at least three capacitors each having a first node and a second node; a plurality of first transistors connected between the first nodes of respective the capacitors and a first power supply, the first transistors charging the first nodes, respectively; a plurality of second transistors connected between the second nodes of respective the capacitors and the first power supply, the second transistors charging the second nodes, respectively; a plurality of third transistors connected between the second nodes of respective the capacitors and an output terminal, the third transistors outputting the electric charge of respective the capacitors to the output terminal; a plurality of fourth transistors each connected between the first node of one of respective the capacitors and the first node of one of the capacitors which is adjacent to the capacitor, each the forth transistor transferring electric charge between the first nodes of respective the capacitors; at least one fifth transistor connected between the first node of one of respective the capacitors and the first node of at least another one of the capacitors which is excluded from the capacitor which is adjacent to the capacitor, the fifth transistor transferring electric charge between the first nodes of respective the capacitors; a detection circuit detecting a boosted voltage output from the output terminal; and a control circuit connected to the detection circuit, the control circuit selectively turning on the fourth transistors so as to serially transfer electric charge between the first nodes of the capacitors adjacent to each other when the voltage detected by the detection circuit is lower than a reference voltage and selectively turning on the first transistors, the fourth transistors, and the fifth transistors so as to parallel transfer electric charge of the first nodes of the capacitors to the first nodes of the capacitors adjacent to each other and the first nodes of the other capacitors when the voltage detected by the detection circuit is higher than the reference voltage.
According to the present invention, electric charge can be effectively utilized by recycling the electric charge of each capacitor. Therefore, the voltage to be supplied to each node from a power supply can be reduced. Thus, electric charge can be effectively utilized in order to obtain a required high voltage, and current consumption can be reduced.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.